The present invention relates to a bone anchor for use in clinical surgery, for example in the treatment of traumatic fractures caused by osteoporosis of bones, among others. The bone anchor has a main body with a head. One or more insertion holes extend from a first opening formed in the head towards a second opening formed in the main body, for example in the head as well or in a shank, wherein the insertion hole has an axis that is generally inclined with regard to a longitudinal axis of the main body. The insertion hole is configured to receive and guide therethrough a pin-shaped element, such as for example a Kirschner-wire, which is to be anchored within the bone or bone fragment under concern.
Such pin-shaped elements may help in preventing a loosening of a bone anchor formed as a bone screw from a bore hole formed in the bone. Due to the inclination of the pin-shaped element with respect to the longitudinal axis of the bone anchor, the head is rotationally fixed and may remain in its position once the pin-shaped elements are inserted through the insertion holes and further introduced into the adjacent bone material.
One example is described in document US 2006/0111720 A1. The surgical screw being disclosed is configured to attach a blocking plate to a bone. The screw comprises two holes inclined with respect to the screw. Each hole receives a surgical nail made of a stainless metal. The inclined holes extend from a hexagonal engagement portion formed in the screw head and open into a transition region between the spherical head and a neck portion of the threaded stem. The surgical nail is of the Kirschner-type. The surgical nail solves spontaneous loosening problems of the surgical screw.
The use of inclined pins is also known from a dental implant described in U.S. Pat. No. 3,579,831. Two pins are guided through inclined bores extending through a shank section in order to stabilize the rotational position of the implant such as to retain the screw reliably in the bone.
Another dental implant is disclosed in U.S. Pat. No. 5,984,681. The implant tapers towards a lower terminal end and comprises an access opening for engagement with a false tooth at its proximal end. A through bore extends from the bottom of the access opening in an inclined fashion with respect to the longitudinal access of the implant. An anchoring pin or screw is received therein which has a threaded self-tapping portion for insertion into the alveolar bone of a patient.
In each of the above described cases, while the implant or bone screw is reliably maintained or stabilized within the adjacent bone material due to the inclined nails, wires or pins, there may still arise a problem that such nails, wires or pins itself may loosen from the bone material in which they are anchored. They may thus lose their capacity of stabilizing or retaining the main body of the respective implant or bone screw.
This problem may particularly become important in cases where the pins, nails or wires function to reposition or fixate fractures of bones or bone fragments, or where these are applied in the arthrodesis of smaller joints, for example.